1. Field of the Invention
This invention relates to a frame which is used for manufacturing light emitting diodes (commonly abbreviated as "LED"). The present invention also relates to a method of using such a frame for efficiently manufacturing LEDs.
2. Description of the Prior Art
Like other electronic components, LEDs are manufactured by using such a frame as shown in FIG. 7 of the accompanying drawings. Usually, the frame has a strip form with a limited length and is known as "leadframe".
As shown in FIG. 7, the frame or leadframe, generally designated by reference numeral 1, is prepared by punching a metal sheet to have a base bar 3 extending longitudinally of the frame and a tie bar 4 also extending longitudinally of the frame in parallel to the base bar 3. The base bar 3 is formed with a plurality of indexing holes 2 which are used for longitudinally transferring the frame 1.
Between the base bar 3 and the tie bar 4, there are multiple pairs of leads 5, 6 arranged at a constant pitch longitudinally of the frame 1. The respective pairs of leads 5, 6 extend beyond the tie bar 4 to provide corresponding pairs of chip bonding cup end 7 and wire bonding end 8. Near the pairs of cup end 7 and wire bonding end 8, the respective leads 5, 6 together by a inforcing bar 4a extending longitudinally of the frame 1 laterally outwardly of the tie bar 4, thereby increasing the supporting rigidity or stability for the respective pairs of cup end 5 and wire bonding end 6.
For manufacturing LEDs, the frame 1 is first introduced into a bonding unit (not shown) in which an LED chip 9 is bonded to each chip bonding cup end 7, as shown in FIG. 8. In the bonding unit, further, a metal wire 10 is bonded to the LED chip 9 and to a corresponding wire bonding end 8. Such a bonding operation is performed individually for the respective pairs of cup end 7 and wire bonding end 8 as the frame 1 is transferred stepwise by utilizing the indexing holes 2.
Then, the frame 1 is introduced into a molding unit (not shown) wherein a resin package (not shown) is formed to enclose each pair of cup end 7 and wire bonding end 8. The resin package may be made of a transparent resin material such as epoxy to have a general shape of a bullet.
Finally, the respective packaged LED devices are separated from the frame 1 by cutting the leads 5, 6 near the base bar 3 and by cutting the tie bar 4 and the reinforcing bar 4a near the respective leads 5, 6. Thus, product LED devices are obtained each of which has a pair of leads 5, 6 extending from the unillustrated resin package.
The prior art described above is disadvantageous at least in the following points.
First, the pairs of cup end 7 and wire bonding end 8 are provided only on one side of the frame 1. Since the spacing or pitch between the respective pairs of up end 7 and wire bonding end 8 must be rendered sufficiently large to enable formation of the relatively bulky resin packages, there is a limitation in increasing the number of obtainable LEDs per unit length of the frame. As a result, the production efficiency lowers, and much portion of a metal sheet is wasted at the time of punching it into the frame, thereby increasing the production cost per LED.
Secondly, since the frame 1 has a strip-form with a limited length, plurality of such frames need be successively transferred and handled in actual manufacture of LEDs. Specifically, at the entrance and exit of each of the different process units (e.g. a bonding unit, a molding unit, and etc.), the frames need be stacked in a frame magazine. Thus, it is necessary to provide some mechanism which individually picks up from or discharge into the frame magazine. It is further necessary to provide some mechanism for transferring the frame magazine between the different process units. As a result, the cost of the manufacturing apparatus is relatively high, but yet the production efficiency is relatively low due to the need for individually handling the strip-like frames.